The Oceans of Contrast: Indian Ocean Gallery features vibrant tropical beauties from the warm Indian Ocean. Exhibits include the very popular interactive Western clownfish (alias Nemo) exhibit, honeycomb eels and a coral exhibit. This gallery also features a 3m-wide cylindrical exhibit showcasing the dazzling colours of Indian Ocean fish.
Rainbow nation on the reef
Most tropical fish are brightly coloured and use colour as flags or advertisements. Some colours warn of danger and others advertise useful cleaning services. Patterns and colours also help to camouflage the fish, making it difficult for predators to see its true shape amongst the corals and sponges. Some fish species mimic others. The mimic blenny imitates the colours and behaviour of the harmless blue cleaner wrasse, but instead of cleaning, it tears flesh from unsuspecting fish waiting for a clean.
Colour also helps to identify "friend" or "foe" on the reef. Many fish are territorial and will chase fish of the same species. Females and juveniles are different in colour and markings so that the male will allow them to feed in his territory.
The mighty Agulhas Current
The Agulhas Current, one of the most powerful currents in the world, flows southwards down the east coast of South Africa, bringing warm Indian Ocean water from tropical regions.
The coastal waters are warm, generally clear and low in nutrients. Diversity is the name of the game on the east coast and a great variety of colourful fish, such as butterflyfish, damsels, surgeons and angelfish add spice to life on the reef.
Although there is great diversity on the east coast, the population size of each species is restricted due to fierce competition for food, limited space on the reef and a high number of predators.
Coral reefs are formed over millions of years and are found in the warm oceans of the world.
Corals are not plants or even rocks. They are colonies of small animals, known as polyps, living closely together with minute single-celled plants called zooxanthellae. This is known as mutual symbiosis as both the corals and the zooxanthellae benefit from the association.
The corals receive "food" from the zooxanthellae when they photosynthesise and in return the corals supply the zooxanthellae with ammonia and phosphate from their waste metabolism.
The transfer of these waste products to the zooxanthellae is crucial for their survival as inorganic nutrients are almost absent in the surrounding water.
Corals under threat
Many of the world’s reefs are under threat.
Coral bleaching is caused by increased sea surface temperature, high levels of ultra-violet light, high turbidity, sedimentation and abnormal salinity. The zooxanthellae living in the polyps die and the corals turn white, becoming more vulnerable to algal overgrowth, disease and reef organisms, which bore into the coral skeleton and weaken the structure of the reef.
Human activities are the major threat to coral reefs. Pollution, overfishing, destructive fishing practices using dynamite or cyanide, collecting live corals for the aquarium and jewellery markets and mining coral for building materials damage reefs.
Poisonous or venomous – what's the difference?
Poisonous animals have poisonous flesh or poison glands in their bodies. These animals do not "inject" the poison, but the poison is transferred if the flesh is eaten or if it comes into contact with the skin. Pufferfish are poisonous animals.
There are more than 80 species of angelfish, 11 of which are found off the coast of southern Africa.
Angelfish are underwater artworks – they have spectacular colours and patterns.
Most angelfish change their colours and patterns as they grow to adulthood. To confuse us even more, the males and females are also differently coloured and marked – so much so that they look like completely different fish!
Angelfish are not such angels – they have a secret weapon in the form of a sharp spine on each gill cover, which they use to defend themselves and to wedge themselves into cracks on the reef.
This is the biggest family of tropical fishes. There are about 120 different species worldwide and about 24 of these live off the southern African shore.
Butterflyfish are so named as they dart to and fro about the reef, just like butterflies flit between plants.
Butterflies have mostly black, yellow and white markings. Several species have a large black dot towards the back of their bodies. This eye-spot supposedly confuses would-be predators.
Most butterflyfish change colour at night and find cracks and crevices on the reef to sleep.
There are 51 species of surgeonfishes, 19 of which occur in southern African waters.
Surgeonfish are so named because of the scalpel-like spines on either side of their tail fins. These spines are folded away into a groove when not in use.
When surgeonfish are threatened or alarmed, the scalpel spines are lifted and used to slash at their attackers! They also use the spines to wedge themselves into cracks in the reef.